Fail-safe speed control system for abrasive wheels



May 10, 1966 A, W, FINKL 3,250,043

FAILVSAFE SPEED CONTROL SYSTEM FOR ABRASIVE WHEELS May 10, 1966 A. W.FINKL.

Filed Aug. 27, 1963 FAIL SAFE SPEED CONTROL SYSTEM FOR ABRASIVE WHEELS 2Sheets-Sheet 2 daf INVENTOR.

United States Patent O 3,250,043 FAIL-SAFE SPEED CONTROL SYSTEM FORABRASIVE WHEELS Anthony W. Finkl, Chicago, Ill., assignor to A. Fink] &Sons Co., Chicago, Ill., a corporation of Illinois Filed Aug. 27, 1963,Ser. No. 304,810 5 Claims. (Cl. 51-134.5)

' This application is a continuation-in-part of my copending applicationSerial No. 282,640, filed-'May 23, 1963.

This invention relates generally to the control of the peripheral speedof a rapidly rotating member. Specifically, it-relates to a system forcontrolling the peripheral speed of a large abrasive cut-off wheel ordisc whereby maximum cutting efficiency is substantially tmaintainedover the entire wheel speed range. In other words, the peripheral speedof the abrasive wheel is maintained close to the maximum safe peripheralWheel speed as the wheel diameter decreases from wear, and the wheelr.p.m. correspondingly increases. t

Accordingly, a primary object of my invention is to provide a controlsystem for large abrasive cut-off wheels or discs.

Another object is to provide such ya control Asystem which maintains theperipheral speed of the wheel close to, or within, a predeterminedmaximum safe peripheral speed range as the wheel r.p.m. is increased dueto wheel wear.

A further object is to provide a control system for an abrasive cut-offwheel or disc in which the r.p.m. of the wheel is automaticallyincreased upon Wear of the wheel to a predetermined point, the increasedr.p.m. resulting in a peripheral speed close to or within the maximumVsafe peripheral speed.

4for maintaining the peripheral speed of an abrasive wheel at or below apredetermined speed limit or range which does not require physicalcontact with the wheel or any related parts of the entire assembly tosense, and control, the wheel speed.

Yet a further object is to provide `a control system for an abrasivewheel or disc which uses a beam of energy, either visible or invisible,to regulate the wheel speed, the beam signal being controlled by thephysical sizeof the wheel itself.

Yet another object is to provide a control system in which the speed ofthe Wheel is automatically controlled without the exercise of anydiscretion by the operator or the necessity of making physicaladjustments by the operator during the useful life of the wheel.

Other objects and advantages of the invention will become apparent froma reading of the following detailed description of a preferredembodiment of the invention.

My invention in the broadest form comprises a system for controlling theperipheral speed of a rotating wheel without physically contacting thewheel or any related parts of the entire assembly. I am aware of priorart attempts to control, and maintain, within predetermined limits, theperipheral speed of an `abrasive wheel, but to my knowledge they allinvolve some form of physical contact with the wheel or parts of thestructure, either direct or indirect.

In my co-pending application Serial No. 282,640, filed May 23, 1963, ofwhich this application is a continua- ICC tion-in-part, I disclose asystem for controlling the peripheral speed of an abrasive wheel bychanging the Wheel housing which involves, in effect, indirect physicalcontact with the wheel.

My present system controls the speed of rotation by sensing the physicalsize of the wheel from a point remote therefrom and thereafter suitablycontrolling the peripheral speed of the wheel in response to the sensedsize of the wheel. In my preferred embodiment, which is disclosed in theaccompanying drawing and explained in detail in the followingdescription, a source of visible or invisible light or other forms ofdirectable energy is so positioned that its path will be interrupted bythe physical presence of the wheel, and, so long as its path isinterrupted, suitable energy activated controls are not able to operateto increase the Wheel r.p.m. In addition to visible and invisible light,such as 'infra-red and ultraviolet, beta and gamma rays may be employedin conjunction with suitable means for responding to the signalsgenerated by the absence or presence of these latter signal generatingsources.

Common to all of the above described systems is the fact that there isno physical Contact, either direct or indirect, between the Wheel sizeand speed measuring and activating mechanism and the wheel itself.

The preferred embodiment of the invention is illustrated more or lessdiagrammatically in the accompanying figures wherein:

FIGURE 1 is a schematic view of my control system;

FIGURE 2 is a detailed view of a portion of my control system; and

FIGURE 3 is a wiring diagram of a preferred embodiment of my invention.

Like reference numerals will be used to refer-to like or similar partsin the following description of the drawmgs.

A wheel or other rotating memberl whose peripheral speed is to becontrolled is indicated at 10 in FIGURE 1. My control system isapplicable to a Wide variety of rotat-ing members but for convenience ofdescription and illustration I will describe my invention in connectionwith a large abrasive cut-off wheel or disc. The origin-al size of tthewheel is indicated at 11. The decrease 4in diameter of the wheel is dueto wear, and the solid line outline of the wheel represents thecondition of the wheel at that point in its life span at which mycontrol system functions to increase the r.p.m.

The wheel is mounted on a shaft 12 by any suitable means 13. The shaftcarries a pulley 14 which is connected by a belt or other powertransmission'member 15 to a drive pulley 16 mounted on the power shaft17 of an electric motor 18. .The electric motor is amultiple speedmotor. For convenience of description a two-speed motor is illustratedand described.

The cut-olf wheel rotates in a Wheel guard or housing indicatedgenerally at 20 which may be bolted or otherwise permanently secured tothe machine frame 21. A pair of apertures 22 and 23 are formed in theopposite side walls of the housing. Means for generating a beam ofenergy is indicated at 24. The means may be a source of visible light oralternatively, and preferably, a source of invisible light lsuch as -asource of infra-red light.

Means for generating an electric current in 4response to reception of abeam of energy from source 24 is indicated at 25. The generating -meansis preferably a photoelectric cell which functions in a well-knownmanner to generate a signal current vupon reception of `a `beam ofvisible or invisible light.

The signal current generated by the photo-electric cell 25 istransmitted to power amplifier 26 which is connected to any suitablepower source, preferably a source of l10- volt alternating current. Thepower ampliiier in turn is 11G-volt alternating current power source.

connected to a fail-safe control circuit for varying the motor speed,the circuit being indicated generally at 27. Three lines, 28, 29 and 30extend from the control circuit to the two-speed motor 18. One of thelines is a common and the other two lines are associated with -a set ofwindings in the motor field, one of the windings being associated with alow-speed circuit and the other winding with a high-speed circuit in amanner well known in the art.

The abrasive wheel and its associated housing is shown in detail inFIGURE 2. Each of apertures 22 and 23 is a hole, slot or other aperturewhose sides diverge upwardly and outwardly from the center of thehousing. The taper of the light aperture aids in preventing entrapmentof dirt and particles worn away from `the wheel and workpiece. A deectorwhich may, for example, be'a shallow cone or dome-s-haped piece of sheetmetal which has an 'aperture 35 at its apex aligned w-ith the light pathextends between the housing apertures 22 and 23. Bolts 36 or othersuitable securing means connect each deiiector by its peripheral lange37 to the housing wall. The lower portion of the `deflector is spacedoutwardly from the housing wall by `a spacer 38. The spacer permits theabrasive dust to fall through, thereby preventing the accumulation ofdust build-up.

A pair of transparent safety covers for the source and pick up of energyare indicated at 40 and `41. Preferably a shatterproof glass or cle-arplastic is employed. Each glass is removably mounted on the outside ofthe wall housing by `a pair of-mounting flanges 42. Each plate or safetycover prevents the escape of grinding dust without interfering with thetransmission of alight beam from one side of the housing to the other.Cover 40 further prevents the photo-electric cell or eye from becomingpitted and eroded from the high speed particles that iiy off theabrasive wheel during engagement with a workpiece. Pitting and erosionof the wheel would ultimately cause loss of light transmission to thephoto-electric cell, thereby preventing eiiicient functioning of thesystem. Should this ever happen, the system will run at low speed aswill later be explained in detail.

The speed control circuit for the motor 18 is shown in detail in FIGURE3. Lines L1 and L2 terminate at a A safety fuse 44 and olf-on switch 45are located in L1. The motor 18 is connected across main power lines L1-and L2 by a pair of lines 30 and 46. Line 46 terminates at a speedswitch 47 which is normally biased into contact with contact 48 in line28. Line 29 terminates in a contact 49. The unotor will operate at highor low speed depending upon which contact speed switch 47 is inoperation.

The source of energy, in lthis instance a source of visible light 24, isconnected directly across lines 46 and 30 and will therefore be onwhenever the off-on switch 45 is closed.

Photo-electric cell 25, which is positioned to pick up the beam ofenergy from source 24, is connected to power arnplitier 26 by a pair ofleads 50 yand 51. The power ampliiier in turn is connected across theline voltage by leads 52 and 53. The output leads 54, 55 from the powerampliiier are connected to the ends of a sensitive solenoid coil 56, thecoil 56 controlling normally open switch 57. The contact side of switch57 is connected by a line 58 through the secondary winding 59 of a lowvoltage circuit control transformer Y60, the primary winding of which isconnected across power lines L1 and L2. The other side of the secondarycoil 59 is connected by line 61 to one end of another solenoid coil 62.The other end of solenoid coil 62 is connected to switch 57 by line 63.Solenoid 62 controls speed switch 47 which is normally biased intocontact with the low lspeed circuit contact 48.

The use and operation of my invention is as follows:

Grinding wheelsv have an optimum peripheral speed, or at least anoptimum peripheral speed range, within which the grinding or cuttingaction of the wheel is most eifective and it is highly desirable thatthe wheel be operated at or close to that operationg speed at all times.As a practical matter, it is impossible to maintain the peripheral speedof the wheel at the optimum speed or speed range if the wheel r.p.m.ismaintained constant. This is because the diameter of the wheel wearsdown with use, particularly where the wheel is employed primairily as acutting tool, such as an abrasive cut-off wheel. As the wheel wears theperipheral speed decreases and optimum cutting efficiency falls off.This problem is especially acute with thin wheels which wear ratherquickly, such as those used for cut-olf yof steel or other high strengthmetals.

The problem of maintenance of an optimum peripheral wheel speed can becured by increasing the rpm. of the wheel as the diameter decreases fromwear. In the prior art this has generally been done by increasing thespeed of the wheel motor, although other schemes such as varying thesize of drive pulleys between the vmotor and the wheel also have beenemployed.

Equipping a grinding wheel with a multiple or variable speed motor hasserious drawbacks, however. If, for example, a new maxi-mum diameterwheel is placed on a spindle and the wheel rotated at the trate of speedintended to be used with a wheel of smaller diameter, the wheel couldphysically break up. Centrifugal explosion resulting in injury to theoperator and damage to the equipment could easily occur. This is aconstant danger because it is entirely possible for an operator toremove a worn, small diameter wheel, which has 'been turned at a maximumr.p.m., and install a new, maximum diameter Wheel, and forget to correctthe motor speed to compensate for the diiierence in wheel diameter. Ifthe motor is then started with the new maximum diameter wheel in place,with the motor speed setting intended for a minimum diameter wheel, itis entirely possible for the wheel to explode causing serious danger tothe operator and the machine.

My invention provides automatic control of the peripheral speed of thewheel, all the while maintaining the peripheral speed at or near theproper speed for optimum cutting eiiiciency.

Further, it is impossible for the wheel, when equipped with myinvention, to be operated at too high a speed because the high speedmotor circuit cannot be energized until the wheel has worn away to apoint at which an increase in r.p.m. will not increase the peripheralspeed of the wheel past a pre-determined safe maximum operating limit.In addition, failure of any component in the control system will resulteither in shut-down of the system gr cutback of the operating speed tothe lowest motor spee Referring now to FIGURE 3, and assuming anabrasive cutting wheel of a size indicated at 11 in FIGURE l isinstalled on wheel shaft 12, closure of the off-0n switch 45 will resultin operation of the two-speed motor 18 at its low speed. The motor isenergized through lines 30 and 46, line 46 terminating in speed switch47 which is in contact with contact 48 in the low speed circuit 28 ofthe motor. The source of energy 24 is likewise energized as itisconnected directly across lines 46 and 30.

The beam of energy, preferably invisible light emanating from source 24,will pass through aperture 23 in the right wall of housing 20. So longas the grinding wheel blocks the path of light between apertures 23 and22 in the housing walls, no signal will be received by thephoto-electric cell 25. As soon as the wheel wears to a diameterindicated in FIGURE 3'however, the photoelectric cell will be energizedsince the light path between apertures 22 and 23 will be uncovered bythe wheel. At this time the peripheral speed of the wheel will beconsiderably less than it was originally even though the r.p.m. isconstant. If the original peripheral speed of the wheel was close to orwithin the safe operating speed, the peripheral speed of the wheel inits FIGURE 3 condition will be somewhat below the safe, optimumoperating speed.

The signal generated by the photo-electric cell 25 is transmitted topower amplifier 26 by the appropriate lead 50 or 51. The power amplifierwill immediately amplify the signal which is then transmitted tosolenoid coil 56. Normally open contact 57 will immediately close.Closure of contact 57 energizes solenoid coil 62 since coil 62 isconnected directly to the output winding of transformer 60 by lines 63,58 and 61. Energization of solenoid coil 62 moves speed switch 47 fromits illustrated position into contact with high speed contact 49.Movement of the switch opens the low speed circuit and energizes thehigh lspeed circuit. The motor speed is immediately increased whichresults in an increase in r.p.m. and consequently the peripheral speedof the grin-ding wheel 10. f

Should any failure occur in any ycomponent of the system other thanlines 28, 29, 30 and speed switch 47 and its associated contacts 48, 49,the motor speed will immediately drop to low, and the grinding wheelwill slow up. Thus, for example, should light 24 burn out, thephoto-electric cell 25 will not generate any signal to the poweramplifier and coil 56 will be de-energized. The de-energization of coil56 will open switch 57 and deenergize coil 62 and the speed switch willreturn to its normal position in contact with low speed contact 48.

Although a preferred embodiment of the invention has been illustratedand several Variations have been specifically described, it will at oncebe apparent to those skilled in the art that further changes may be madeWithout departing from the spirit of my invention. Accordingly, it

is my intention that my invention be limited not by the foregoingexemplary description but solely by the s-cope of the hereafter appendedclaims considered in view of the pertinent prior art.

I claim:

-1. A fail-safe control system for large abrasive cut-olf wheels ordiscs which are powered by a motor having a high speed contact and a lowspeed contact, said system including, in combination,

a low speed circuit connecting the low speed contact of the motor toasource of power,

:said low speed circuit having a speed switch therein which is normallybiased to complete the circuit,

a high speed circuit connecting the high speed cont-act of the motor tothe speed switch when the speed switch is biased to a position in whichthe high speed circuit is completed, and the low speed circuit isopened, and

means for completing the high speed circuit to thereby increase ther.p.m. of the abrasive wheel upon wear of the wheel to a predetermineddiameter smaller than the original diameter,

said means including an energy source which generates an axiallydirected beam of energy, of substantially constant diameter at anyconvenient distance from the wheel,

a photo-electric cell energizable upon the reception of the beam ofenergy,

said energy source and photo-electric cell flanking the abrasive wheeland being so positioned with respect to one another that the wheel willprevent reception of the beam by the photo electric cell until the wheelhas worn to a diameter such that the peripheral speed of the wheel whenrotated at high speed will be Within a pre-determined maximum safespeed,

a power amplifier connected to a source of power and to thephoto-electric cell,

coil means connected to the power amplifier and associated with thespeed switch,

, ously decrease in size as it works, said system including,

in combination,

first circuit means effective, when energized, to operate :saidmulti-speed motor at a low speed,

second circuit means effective, when energized, to op crate said motorat a higher speed,

means for generating and receiving an axially directed beam of energy ofsubstantially constant width,

said means for generating the beam of energy and the means for receivingit, being located outside a wheel guard,

the wheel guard having apertures which enable the beam, in the absenceof the wheel or disc to pass therethrough, l

the wheel guard apertures being inclined toward the taxis of rotation ofthe wheel, and inwardly toward one another, to thereby reduce entrapmentof dust,

said wheel or disc being so positioned so as to interrupt the beam untilthe wheel or disc wears a pre-determined amount, and

means for energizing the second circuit means upon reception of theaxially directed beam of energy by a receiver associated with the secondcircuit means.

3. The system of claim 2 further characterized in that at least one ofthe apertures has an interiorly positioned dust deilector guard carriedby an associated Wall of the wheel guard, at least the lower portion ofthe defiector guard being spaced away from the wall to thereby enabledust to fall through whereby dust build-up is prevented.

4. A system for varying, in discontinuous increments, the speed ofrotation of a multi-speed motor which drives an abrasive wheel or disc,which wheel or disc continuously decreases in size as it works, saidsystem including, in combination,

first circuit means effective, when energized, to operate saidmulti-speedmotor at a low speed,

second circuit means effective, when energized, to operate said motor ata higher speed,

means for generating an axially directed beam of energy of substantiallyconstant width,

means for receiving said axially directed 'beam of energy,

-said wheel or disc being so positioned as to interrupt the aforesaidbeam until the wheel'or disc wears a predetermined amount,

means for translating the received axially directed beam of energy intoa control signal, and

means for energizing the second circuit means and deenergizing the firstcircuit means upon reception of the control signal derived from theaxially directed beam of energy.

5. The system of claim 4 further characterized in that the means forgenerating the beam is a source of visible light.

References Cited by the Examiner UNITED lSTATES PATENTS 766,229 8/ 1904Douglas 51--134-.5 2,994,994 8/ 19611 Lonaberger 51-1345 3,113,40512/196-3 Schneider et al. 51-134.5

LESTER M. SWINGLE, Primary Examiner,

I. SPENCER OVERHOLSER, Examiner.

J. L. TATE, Assistant Examiner.

1. A FAIL-SAFE CONTROL SYSTEM FOR LARGE ABRASIVE CUT-OFF WHEELS OR DISCSWHICH ARE POWERED BY A MOTOR HAVING A HIGH SPEED CONTACT AND A LOW SPEEDCONTACT, SAID SYSTEM INCLUDING, IN COMBINATION, A LOW SPEED CIRCUITCONNECTING THE LOW SPEED CONTACT OF THE MOTOR TO A SOURCE OF POWER, SAIDLOW SPEED CIRCUIT HAVING A SPEED SWITCH THEREIN WHICH IS NORMALLY BIASEDTO COMPLEWTE THE CIRCUIT, A HIGH SPEED CIRCUIT CONNECTING THE HIGH SPEEDCONTACT OF THE MOTOR TO THE SPEED SWITCH WHEN THE SPEED SWITCH IS BIASEDTO A POSITION IN WHICH THE HIGH SPEED CIRCUIT IS COMPLETED, AND THE LOWSPEED CIRCUIT IS OPENED, AND MEANS FOR COMPLETING THE HIGH SPEED CIRCUITTO THEREBY INCREASE THE R.P.M. OF THE ABRASIVE WHEEL UPON WEAR OF THEWHEEL TO A PREDETERMINED DIAMETER SMALLER THAN THE ORGINAL DIAMETER,SAID MEANS INCLUDING AN ENERGY SOURCE WHICH GENERATES AN AXIALLYDIRECTED BEAM OF ENERGY, OF SUBSTANTIALLY CONSTANT DIAMETER AT ANYCONVENIENT DISTANCE FROM THE WHEEL, A PHOTO-ELECTRIC CELL ENERGIZABLEUPON THE RECEPTION OF THE BEAM OF ENERGY, SAID ENERGY SOURCE ANDPHOTO-ELECTRIC CELL FLANKING THE ABRASIVE WHEEL AND BEING SO POSITIONEDWITH RESPECT TO ONE ANOTHER THAT THE WHEEL WILL PREVENT RECEPTION OF THEBEAM BY THE PHOTO ELECTRIC CELL UNTIL THE WHEEL HAS WORN TO A DIAMETERSUCH THAT THE PERIPHERY SPEED OF THE WHEEL WHEN ROTATED AT HIGH SPEEDWILL BE WITHIN A PRE-DETERMINED MAXIMUM SAFE SPEED, A POWER AMPLIFIERCONNECTED TO A SOURCE OF POWER AND TO THE PHOTO-ELECTRIC CELL, COILMEANS CONNECTED TO THE POWER AMPLIFIER AND ASSOCIATED WITH THE SPEEDSWITCH, SAID COIL MEANS, WHEN ENERGIZED BY A SIGNAL FROM THE POWERAMPLIFIER, BEING OPERABLE TO BIAS THE SPEED SWITCH TO A POSITION INWHICH IS COMPLETES THE HIGH SPEED CIRCUIT, AND OPENS THE LOW SPEEDCIRCUIT.